About Repsquidge
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Introduction

Repsquidge maintains replicas of directory trees as a form of backup.

A replica of a directory tree is a complete copy of the tree, with identical modes, permissions, ownerships and modification dates. A replica set is a collections of such replicas, with the exception that files which are identical in multiple replicas are maintained as hard links, so that there is only one file taking storage space. Repsquidging is the process of adding a new replica to a replica set, linking to files which are unchanged from a previous replica, and copying new and modified files.

Backups with repsquidge

Repsquidge provides protection against file loss by keeping backup copies of files. This can help recover from user error, administrator error, hardware failure, and other causes of file loss.

Here is a typical repsquidge backup scenario.

A fileserver server NFS exports a filesystem /home, containing users' home directories, which we want to back up. This is then NFS mounted on another machine, backup, which has two hard disk drives and a tape drive. Every morning at 3am, repsquidge runs on backup, and adds a new replica of server:/home to the replica set on one of its disks. The disk used alternates morning to morning, so that two separate replica sets are maintained. Thus, if one disk fails, half of the replicas are still available. Periodically, selected replicas are dumped to tape for archiving and offsite backup purposes.

There are a number of advantages in using repsquidge over traditional tape backups:

  • no tapes to change every day
  • faster backups
  • faster access to backups
  • no messing with incremental backups
Of course, some of these depend on the particular hardware and network you're using.

There are some disadvantages as well:

  • extra backup capacity is more expensive (hard drives versus tapes)
  • backups are not as secure, since hard drives stay in the machine
Replica ageing

Even with the space-saving of repsquiding, you'll eventually run out of disk space if you keep all your replicas.

Repsquidge provides replica ageing, which is the automatic and configurable removal of selected older replicas.

For example, repsquidge can be configured to keep at most 5 replicas less than a week old, 4 replicas less than a month old (but older than a week), and 4 replicas less than a year old (but older than a month). Replicas are selected for removal so that there is a good spread of dates kept.

Furthermore, you can define which days' replicas are most important, and should be kept in preference to other days' replicas. For instance, Saturday's replicas (backing up a week's work to Friday) are often the most important to keep.

 

Trinity College Software

Tim Bell
Last modified: Wed Jun 21 15:36:25 EST 2000